1. Field of the Invention
The present invention relates to a driving apparatus for a slide in a press machine which reciprocates up and down.
2. Description of the Related Art
There is a conventional press machine which attains a precise press and an efficient production, because of a slide which decreases its down-speed beyond certain level from a bottom dead center which means the lowest position of the slide through its reciprocal movement. Such systems as using a slip element (described in Japanese Utility Model Application Laid-open No. 1-40634) and an eccentric link (described in Japanese Patent Application Laid-open No. 62-275599) are well-known in this art. The slip-element type system is schematically shown in FIGS. 4 and 5. The eccentric-link type system is shown in FIGS. 6 and 7.
In FIGS. 4 and 5, a pinion 51 is driven by a motor as a drive source and fits into a main gear 52. A lever 53 opposite the main gear 52 is fixed to one end of a crankshaft 54 of which an eccentric portion 54A is connected with a slide 56 by means of a connecting rod 55 that comes in therebetween. The lever 53 has a long guide groove 53A on its surface so that a slip element 58, on a forward end of a rotation axle 57 provided on the main gear 52, can move along the guide groove 53A. A rotation axis O.sub.6 for the main gear 52 is offset from a rotation axis O.sub.7 for the lever 53 (an axis of the crankshaft 54 as well) by e.sub.3.
When the main gear 52 is rotated by the pinion 51, the slip element 58 moves the lever 53 and the crankshaft 54 to translate the slide 56 either upwardly or downwardly. AS shown in FIG. 5, when the lever 53 is rotated around the axis O.sub.7 at an angle of 180 degrees from a position shown in solid line to another position 53' shown by dotted line, the main gear 52 will rotate round the axis O.sub.6 at an angle of .theta..sub.3. Following this shift, if the lever 53 is further rotated at an angle of 180 degrees so as to return to the solid line position, the main gear 52 will rotate at an angle of .theta..sub.4. Since the axis O.sub.7 differs from the axis O.sub.6, the angle .theta..sub.3 is less than 180 degrees and the angle .theta..sub.4 is greater than 180 degrees. Accordingly, if the main gear 52 constantly rotates and the slide 56 stays at its bottom dead center when the lever 53 is at the solid line position, it will not take more time for the slide 56 to move from its bottom dead center to top dead center (that is, to move upwardly) than to move from its top dead center to bottom dead center (that is, to move downwardly). In consequence, the upward motion of the slide is quick.
The following explanation for the eccentric-link type system is made with reference to FIGS. 6 and 7. Therein, a pinion 61 driven by a motor, as a drive source, fits into a main gear 62 which turns by means of a set of bearings 63. A rotating crankshaft 64 mounted to bearings 63 is connected to a slide 66 by means of a connecting rod 65. The connection between the crankshaft 64 and the connecting rod 65 is made with an eccentric portion 64A. A yoked type lever portion 64B is provided on a surface of the crankshaft 64 between the bearings 63 and is connected to a yoked type main portion 62A of the main gear 62 by means of a link 67 which is joined with these two portions by pins 68 and 69. A rotation axis O.sub.8 for the main gear 62 is offset from a rotation axis O.sub.9 for the lever portion 64B (an axis of the crankshaft 64 as well) by e.sub.4.
When the pinion 61 drives the main gear 62, this motion will be transmitted to the crankshaft 64 via link 67 and lever portion 64B so as to move the slide 66 upwardly or downwardly. In FIG. 7, when the pin 68 of the crankshaft 64 is rotated round the axis O.sub.9 at an angle of 180 degrees and consequently shift to a position 68' drawn by dotted line, that is, when the crankshaft 64 is rotated at an angle of 180 degrees, the pin 69 of the main gear 62 will shift from a position drawn by solid line to another position 69' drawn by dotted line on the axis O.sub.8. In this situation, a rotation angle of the main gear 62 becomes .theta..sub.5. Following this change in position, when the crankshaft 64 further turn at an angle of 180 degrees so that both the pins 68' and 69' return to the solid line positions, respectively, a rotation angle of the main gear 62 becomes .theta..sub.6. Since the axis O.sub.9 differs from the axis O.sub.8, the angle .theta..sub.5 is less than 180 degrees and the angle .theta..sub.6 is greater than 180 degrees. Accordingly, if the main gear 62 constantly rotates and the slide 66 stays at its bottom dead center when the pins 68, 69 are at the respective positions shown by solid line, it will not take more time for the slide 66 to move from its bottom dead center to top dead center (that is, to move upwardly) than to move from its top dead center to bottom dead center (that is, to move downwardly). In consequence, the upward motion of the slide is quick.
FIG. 8 shows a slide motion denoted by "P" in the slip-element type system drawn in FIGS. 4 and 5 and a slide motion denoted by "Q" in the eccentric-link type system drawn in FIGS. 6 and 7. In FIG. 8, each phase angle of the crankshafts in both systems is adjusted so that both curve lines of the motions P and Q overlap one another from the top dead center to the bottom dead center of the slides. In the eccentric-link type system, when the rotation of main gear 62 is transmitted to the crankshaft 64 via the link 67, the rotation speed of the crankshaft 64 is varied from fast to slow, because of a constant angle swing round the pin 69. Accordingly, if the link 67 is disposed such that the slow down of the rotation speed of the crankshaft 64 occurs when the slide is almost at bottom bead center, the tilted angle (which shows a speed of the slide) of the motion Q.sub.11 is less than that of the motion Q.sub.10. Hence, the curve line of the motion Q becomes like a bottom shape of a wok (a deep round pan).
Because of such a curved slide motion Q, the slide speed in processing (pressing) becomes slow, so that a drawing press will work reliably to produce goods.
However, in the above-mentioned slide driving apparatus employing the eccentric-link type system, the following problems occur.
In FIG. 7, a circle denoted reference numeral E, around an axis O.sub.8, defines a drive rotation locus of the center portion where the main gear 62 and the link 67 are connected one another by the pin member 69 when the main gear 62 rotates once. A circle denoted by reference numeral F, around an axis O.sub.9, is a driven rotation locus of the center portion where the lever portion 64B of the crankshaft 64 and the link 67 are connected to one another by the pin member 68. FIG. 11 shows a swing angle .beta. of the link 67, when one rotation of the main gear 62 is transmitted to the crankshaft 64 as described in FIGS. 6 and 7. A length L caused by the swing angle .beta. can vary the rotation speed of the crankshaft 64 from fast to slow so as to trace the slide motion Q. While the link 67 moves such that the both end portions thereof trace the locus E and F respectively and swings at angle .beta. corresponding to one rotation of the main gear 62, the rotation speed of the crankshaft 64 fluctuates along a curve line G shown in FIG. 9, so that the speed of the slide 66 is effected by the fluctuated rotation of the crankshaft 64, which is described by a curve H in FIG. 10.
In FIG. 9, maximum rotation speed of the crankshaft 64 is V.sub.1 and minimum speed is V.sub.2. High precise pressing by the slide motion Q, as shown in FIG. 8, requires the tilted angle .theta..sub.11 to be less than a certain value. To obtain such a tilted angle .theta..sub.11, the ratio V.sub.1 /V.sub.2 should be high because V.sub.1 means high rotation speed of the crankshaft 64 owing to swing of the link 67 and V.sub.2 means low rotation speed. But, according to the conventional eccentric-link type system, a difference in length between a radius R.sub.3 of the drive rotation locus E and a radius R.sub.4 of the driven rotation-al locus F is made large to keep the locus F inside of the locus E, so that the link 67 does not interfere with any other member while swinging. From a different view, the link 67 is made to have a certain length and be tilted toward the rotation direction so that the rotation of the main gear 62 is transmitted to that of the crankshaft 64. Accordingly, in order to increase V.sub.1 /V.sub.2 to the certain value and obtain the length L by the angle .beta., the eccentric distance e.sub.4, shown in FIGS. 6 and 7, should be long.
For these reasons, the rotational diameter of the above mechanism utilizing an eccentric portion is large, resulting in an unnecessarily large apparatus.
An object of the present invention therefore is to provide a miniaturized slide driving apparatus a miniaturization of the by miniaturizing a diameter of the rotation center portion.